In code division multiple access (CDMA) networks, the mobile stations share a reverse link channel and may transmit simultaneously on the reverse link channel to a radio base station. Common rate control is one technique used to control the load at the radio base station. With common rate control, all mobile stations that need to transmit data on the reverse link are allowed to do so. Each mobile station initially begins transmitting at a specified minimum rate (sometimes called the autonomous rate) and then, depending on load at the radio base station, is allowed to vary its transmission rate. The radio base station periodically estimates the reverse link load and compares the estimated reverse link load to a target load. If the measured load is below a target threshold, the radio base station commands the mobile stations in its cell or sector to increase their transmission rate. Conversely, if the measured load is above the target threshold, the radio base station commands the mobile stations to decrease their transmission rate. In some systems, the radio base station may command the mobile stations to hold their current transmission rate.
With common rate control, the radio base station broadcasts a single up/down/hold rate control command to all mobile stations in a cell or sector and all of the mobile stations respond to the extent that they are able. That is, when a radio base station commands the mobile stations in a cell or sector to increase their transmission rate, all mobile stations in the cell or sector except those already transmitting at maximum power will increase their transmission rate. When a radio base station commands the mobile stations in a cell or sector to decrease their transmission rate, all mobile stations except those already transmitting at minimum power will decrease their transmission rate. Thus, common rate control results in significant fluctuations in load at the radio base station because many mobile stations are changing their data transmission rates at the same time.
The anticipated fluctuations in load are taken into account when setting the target load. The target load is typically selected to balance system throughput against the probability of outages. An outage is considered to occur when the power required to maintain minimum signal quality standards is greater than the maximum transmit power of the mobile station. As an example, a service provider may set the target load so that the frequency of outages is below a predetermined threshold, e.g., 1%. In general, minimizing fluctuations in load at the radio base station would enable the target load to be set higher while maintaining desired service quality objectives.